The present invention relates to acoustic surface wave and acoustic interface wave devices. The term `acoustic surface waves` will be used hereinafter to include acoustic interface waves as well as acoustic surface waves.
Acoustic surface wave devices are being proposed for an increasingly large number of electronic purposes, and acoustic surface wave filters and delay lines are likely to find important applications in the future. Such devices commonly comprise a transducer for launching acoustic surface waves along a predetermined track (which must be along a surface or an interface of a material capable of supporting acoustic surface waves, but need not have any other particular configuration or boundaries) and at least one other transducer for detecting the acoustic surface waves and generating electrical signals in response to the acoustic surface waves. The transducers used conventionally comprise interdigitaled comb-like electrodes. If such electrodes are deposited on a piezoelectric material, the application of alternating electric signals of suitable frequency across the electrodes will tend to propagate an acoustic surface wave orthogonal to the interleaved digits of the comblike electrodes. Conversely, the passage of an acoustic surface wave orthogonal to the digits will induce a corresponding alternating electrical signal between the electrodes. It is also known that such transducers can operate effectively on an electrostrictive material, if a biassing electric field is applied to the material under the transducers. The transducers may be designed to achieve filtering effects.
It is an object of the invention to provide means for coupling acoustic surface waves, so that a desired portion or substantially all of the energy in an acoustic surface wave in a first region can be transferred to acoustic surface waves in a second region. A further object of the invention is to form various novel devices incorporating one or more of such coupling means which form components having useful properties, and may be used either to achieve novel or improved technical effects or as alternatives to known electronic components.